Method of preparing an optical fiber with multiple lenses to optimize coupling with a phototransducer, and an optical system obtained thereby

Abstract

The present invention relates to a method of preparing an optical fiber for optimum coupling with a phototransducer, comprising the following steps: cleaving an end surface on an optical fiber; and depositing a succession of convex lenses on said cleaved surface over the core of the fiber, the lenses being in axial alignment and of decreasing radii of curvature on going away from the fiber. The present invention also provides a system obtained by implementing the method.

We claim: 
     
       1. A method of preparing an optical fiber for optimum coupling with a phototransducer, comprising the following steps: cleaving an end surface on an optical fiber; and   depositing a succession of convex lenses on said cleaved surface over the core of the fiber, the lenses being in axial alignment and of decreasing radii of curvature on going away from the fiber.   
     
     
       2. A method according to claim 1, wherein the various lenses are deposited on the cleaved surface by successively reiterating the following sequence of steps as many times as there are required lenses: a) stretching a length of optical fiber;   b) aligning the resulting tip on the axis of the core of the fiber for the first lens, and subsequently on the axis of the front lens, and making contact with a small amount of pressure;   c) surface welding the tip that has been put into contact;   d) applying traction to the tip to leave behind a calibrated needle; and   e) making a lens by controlled melting of the needle obtained in this way.   
     
     
       3. A method according to claim 1, including the step of depositing at least two lens in succession. 
     
     
       4. A method according to claim 1, including the step of depositing a number of lenses greater than two. 
     
     
       5. A method according to claim 1, wherein the radius of curvature of the lenses is less than a few tens of micrometers. 
     
     
       6. A method according to claim 1, further consisting in placing an element of graded index multimode fiber in line with the optical fiber and in depositing the lenses on a cleaved face of said element of graded index multimode fiber. 
     
     
       7. A method according to claim 1, further comprising the step of placing a piece of step index multimode fiber in line with the element of graded index multimode fiber and in placing the lenses on said length of step index multimode fiber. 
     
     
       8. A method according to claim 6, wherein the radii of curvature of the lenses lies in the range 10 μm to 100 μm. 
     
     
       9. An optical system comprising a phototransducer coupled to an optical fiber, obtained by implementing the method according to claim 1. 
     
     
       10. A system according to claim 9, including at least two lenses. 
     
     
       11. A system according to claim 9, including a number of lenses greater than two. 
     
     
       12. A system according to claim 9, wherein the radius of curvature of each lens is less than a few tens of microns. 
     
     
       13. A system according to claim 9, including an element of graded index multimode fiber interposed between the set of lenses and the monomode fiber. 
     
     
       14. A system according to claim 13, further including a piece of step index multimode fiber between the set of lenses and the element of graded index multimode fiber. 
     
     
       15. A system according to claim 13, wherein the radii of curvature of the lenses lie in the range 10 μm to 100 μm.